Direct growth of single- and few-layer MoS2 on h-BN with preferred relative rotation angles (1504.06641v3)

Abstract: Monolayer molybdenum disulphide (MoS2) is a promising two-dimensional direct-bandgap semiconductor with potential applications in atomically thin and flexible electronics. An attractive insulating substrate or mate for MoS2 (and related materials such as graphene) is hexagonal boron nitride (h-BN). Stacked heterostructures of MoS2 and h-BN have been produced by manual transfer methods, but a more efficient and scalable assembly method is needed. Here we demonstrate the direct growth of single- and few-layer MoS2 on h-BN by chemical vapor deposition (CVD) method, which is scalable with suitably structured substrates. The growth mechanisms for single-layer and few-layer samples are found to be distinct, and for single-layer samples low relative rotation angles (<5 degree) between the MoS2 and h-BN lattices prevail. Moreover, MoS2 directly grown on h-BN maintains its intrinsic 1.89 eV bandgap. Our CVD synthesis method presents an important advancement towards controllable and scalable MoS2 based electronic devices.

Direct Growth of MoS on h-BN via CVD: Mechanisms and Implications

The paper "Direct growth of single- and few-layer MoS on h-BN with preferred relative rotation angles" conducted by Yan et al. applies chemical vapor deposition (CVD) techniques to synthesize molybdenum disulfide (MoS) directly on hexagonal boron nitride (h-BN) substrates. The motivation behind this research is to develop scalable methods for creating high-quality 2D heterostructures suitable for electronic applications, particularly with MoS's direct-bandgap semiconductor capabilities.

Methodology and Growth Mechanisms

The research delineates the intricacies underlying the growth mechanisms of MoS on h-BN, identifying two distinct pathways. For single-layer growth, the paper shows a predominant occurrence of low relative rotation angles (< 5°) between MoS and h-BN lattices, indicating a van der Waals epitaxy modified by lattice mismatching and additional factors. MoS directly grown on h-BN via CVD maintains its intrinsic 1.89 eV bandgap, closely resembling the free-standing MoS bandgap, which demonstrates the pristine electronic conditions offered by h-BN substrates.

For multi-layer growth, the observed formation mechanisms diverge into screw-dislocation-driven (SDD) growth and layer-by-layer (LBL) growth. SDD involves low supersaturation conditions, generating helical structures due to vertical nucleation site dislocation, while LBL sustains by expanding existing single layers vertically under specified growth conditions.

Characterization and Numerical Results

Atomic force microscopy and transmission electron microscopy enable the exploration of MoS's surface topographies and crystallographic features at the atomic level. PL measurements reveal MoS grown on h-BN exhibits strong, narrow PL peaks, indicating a less perturbed electronic environment. Specifically, the peak centered at 1.89 eV supports high quality and reliable MoS device fabrication from such heterostructures.

Implications for Device Fabrication

The findings provide substantial implications for 2D material integration within electronic devices. MoS's robust electronic properties when grown on h-BN suggest potential for creating flexible, stable electronic and optoelectronic devices. The preferred orientation angles between MoS and h-BN in single layers can influence band structure modifications, thereby allowing for tunable electronic applications.

Future Research Directions

Emerging from this research are opportunities to scrutinize the electronic interactions in MoS/h-BN heterostructures with different relative alignments—essential for enhancing device functionalities and efficiency. Additionally, optimizing the growth conditions for multi-layer MoS may expand applicable domains, promoting theory-aligned experimental efforts and fostering advancements in scalable nanofabrication processes.

This paper establishes a foundational step towards controllable and scalable growth of MoS-based devices, heralding further exploration into interfacial engineering and hybrid 2D material applications in next-generation electronic systems.